Start by preheating your oven to 375°F. Place the chicken breasts on a baking sheet and season them with salt and pepper. Roast the chicken in the oven for about 20-25 minutes or until they are fully cooked. Remove the chicken from the oven and let it cool.
Once the chicken has cooled, shred it into small pieces using a fork or your hands.
In a large pot or Dutch oven, heat the olive oil over medium heat. Add the chopped onion and minced garlic and saute for about 2-3 minutes or until the onion is translucent.
Add the chicken broth, diced tomatoes, black beans, corn, green chilies, chili powder, ground cumin, and shredded chicken to the pot. Stir everything together until it's well combined.
Bring the soup to a boil over high heat. Once it starts boiling, reduce the heat to low and let the soup simmer for about 30 minutes or until the vegetables are tender and the flavors have melded together.
Once the soup is done, ladle it into bowls and garnish with tortilla strips, shredded cheese, and a dollop of sour cream.